The present invention relates to a design and construction of a cryoprobe tip for freezing tissues. In particular, the present invention relates to a specific cryoprobe tip configuration and methods of application allowing an improved application of refrigerant that combines direct (spray) and indirect (closed tip) contact of the selected refrigerant with the target tissue in a timely manner. Also, the present invention provides a plurality of interchangeable tips for a better adaptation to the tissue configuration and location.
Cryosurgery is a well-established surgical method which is useful in the treatment of many conditions and which involves the application of extreme cold to tissues to effect freezing of the tissues. The instruments used are, in general, of two types. In the spray tip, the refrigerant is sprayed directly onto the tissue to be frozen. In the closed tip, the cryogenic fluid is confined within the tip. The refrigerant is delivered to a portion of the tip that is inserted into the tissue. Selection of a particular instrument depends on multiple parameters among which are location and volume of the lesion, cost-efficiency ease of application, time spent on application and predictability of freezing effects.
The closed tip probe may use a low boiling point refrigerant like liquid Nitrogen (LN2) or Joule Thomson expansion of fluids like Nitrous Oxide (N2O) or Carbon Dioxide (CO2), or Argon gas. Other techniques include using the latent heat of vaporization, as with Freon, or precooled gas and liquids. Exemplary liquids include chlorodifluoromethane, polydimethylsiloxane, ethyl alcohol, HFC""s such as AZ (50-50 mixture of difluoromethane and pentafluoroethane, sold by Allied Signal), and CFCs such as DuPont""s Freon. The cold generated by a cryogenic fluid is confined to the area of the probe tip where heat transfer occurs across the tip to the surrounding tissues to form an ice ball of frozen tissue. This method has the advantage of locating the frozen zone more precisely and permitting interstitial freezing of tissues by inserting the probe tip deep into the tissue.
But the main drawbacks are that the probe tip usually does not reach the lowest temperature permitted by the refrigerant, due to the less effective heat conductivity of the tip material, forcing the operator to use low boiling point refrigerants. Using these refrigerants requires changing the probe location within the tissue and/or using multiple probes simultaneously to complete the freezing process if a target tissue is more than a few cubic centimeters. Also the miniaturization of modern instruments required by the endoscopic or catheter-based applications requires safe, quick, and efficient cryoprobes which are very small and flexible.
Other drawbacks are that these systems are often bulky and not easily movable from one location to the other, nor are they well suited to use outside of a formal operating room or in minor surgical procedures due to their cost and maintenance requirements.
In contrast, open end, or spray type tips commonly used are less expensive and disposable hand held systems. Advantages of the spray technique are the higher thermal efficiency and the capability of covering a larger area than the closed tip cryoprobe. The tips are used generally for superficial and/or external cryotreatments. Examples of these types of systems include U.S. Pat. No. 3,534,739 to Bryne and U.S. Pat. No. 3,823,718 to Tromovitch. Such devices apply the refrigerant directly to the tissue via a spray nozzle without any contact of the tip with the tissue.
Usually, the operator estimates the effect of cryosurgery by the appearance of tissue as it freezes. At times, when facing large or malignant lesions the operator uses invasive monitoring techniques of the freezing effects using thermocouple or impedance needles inserted into the target tissue, which are not practicable or desirable everywhere. Such devices are potentially hazardous because of the risk of spreading malignant cells. Noninvasive monitoring may be employed, including X-ray, CT, Ultrasonography, or MRI. U.S. Pat. No. 5,069,223 discloses several electrodes/sensors which may be used to evaluate freezing effects in tissue.
The procedure of the simple viewing of the frozen tissue via an endoscope has been recently advocated as a method of application of cryosurgery. U.S. Pat. No. 5,846,235 describes such an endoscopic application using this very unreliable method of monitoring. However, spray tips are not suitable for use in procedures performed within the body due to the difficulty in controlling the amount of cryogen released and the effects of overspray on surrounding tissues.
The prior art is lacking any suggestion of a cryosurgical probe or group of probes with the capability of being used during the same operation to the same tissue, in a dual action mode, i.e. as a closed end and a spray tip type probe. U.S. Pat. No. 4,211,231 describes interchangeable cryotips for successive applications of the different modes of freezing.
Also absent in the prior art is any suggestion that such a system can be used in interstitial freezing of tissues. The reason is that interstitial expansion of gas or liquid refrigerant could be harmful to tissues by forcing gas bubbles under pressure into the tissue with the risk of inflating it or embolizing an open vessel. Our invention avoids this risk by a two-steps method of freezing the tissues using a dual action mode.
Moreover, there is no reference to the use of N2O, or CO2 as particularly suited for the treatment of malignancies, with the exception of some palliative treatments, or on masses of tissue larger than a few cubic centimeters. The usual procedure is to treat these lesions with LN2, Argon, or other powerful refrigerants, such as gas mixtures in cryocoolers with mono or multiprobe systems.
Also absent in the prior art is the regulation of flow of refrigerant in the spray tip type probe and electrical monitoring of the ice ball, which is effected in our invention by an electrical method as described in U.S. patent application Ser. No. 09/429,810 entitled Method and Apparatus for Monitoring Cryosurgical Operations filed Oct. 29, 1999 incorporated herein by reference, also referred to as Cryosurgical Imaging System (CIS).
Another major feature of this invention is that such a contact spray technique solves two main issues in cryosurgery:
a. the alleged need of powerful refrigerant for treating malignant tumors and the temperature needed for destruction of tissues, normal, benign, or malignant, and
b. the necessary use of powerful refrigerants, such as LN2, Argon gas, or mixed refrigerant, in very small closed-end probes, under 3 mm in outer diameter, to get sufficient power efficiency. These small probes are more and more in use every day due to the rapid expansion of endoscopic, percutaneous and minimally invasive surgical procedures.
Conventionally, powerful refrigerants were thought necessary because of the demonstrated effectiveness of fast freezing and large ice ball created by higher thermal gradients. Recently, Rubinsky and Degg, Proc., R. soc. Lond. B234, 343-358 (1988), have shed new light on the process of freezing in tissue. The results show that tissue can be destroyed by freezing to temperature as high as xe2x88x922 degrees C., and that conventional temperatures as low as xe2x88x9250 degrees C. are not required for tissue destruction, if the freezing process is done in such a manner as to insure destruction of the vasculature network.
These findings tend to suggest the use of slower freezing techniques, thus the possible use of medium powered refrigerants, like N2O, and they focus the monitoring more on the vascular bed modifications than through the direct or indirect cell alterations. A real time monitoring of vascular freezing, whatever is the nature of the target tissue is precisely the result obtained by the use of one embodiment of our invention. A recent experimental study (xe2x80x9cBioelectrical impedance Imaging for monitoring cryosurgeryxe2x80x9d, Presentation to the first European Congress of Cryosurgery, San Sebastian, Spain, 30th Mar. 2 Apr. 6, 2000, P. Le Pivert et al.) confirms the existence of different destructive temperature for different tissues, and cryonecrosis at temperature higher than the usually recommended xe2x88x9250 degrees C. It confirms also the efficacy of complex impedance measurements to predict the extent of electrical modifications of frozen tissues related to vascular obliteration and to delayed cryonecrosis.
There remains a need for an alternative means of topical or interstitial application of cryosurgery for the treatment such as hemostasis, ablation, or other cryotreatment of healthy or diseased tissues, having the following characteristics:
1) An ability to be used in contact with the tissue over a larger area than normally available with a usual closed end tip probe using the same refrigerant;
2) An ability to safely fulfill the required task whether it is hemostasis, ablation, or other cryotreatments;
3) Affordability; and
4) Technique simplicity.
It is thus an objective of the invention to provide an alternate improved cryotip system, which combines the advantages of the closed end and open-end techniques, in surface and/or in interstitial applications of cryosurgery, and characterized in that it fulfills most if not all of the criteria noted above.
It is a further objective to provide different refrigerant and different refrigerant sources to connect with such a closed (contact)-open (spray) end tip system.
It is a further objective to provide different methods of application of such a contact-spray tip cryoprobe for different types of tissuexe2x80x94benign or malignantxe2x80x94and different tissue location within the body.
And it is still a another objective to provide a complete cryosurgical system using N2O or CO2 as the refrigerant, a Joule-Thomson effect into the cryotip, and an electrical monitoring system allowing control of the efficacy, in real time, of the probe, or group of probes and the optimal flow rate of gas/liquid mixture into the expansion chamber of the contact-spray tip.
Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.